Engine operating parameters such as air-fuel ratio, spark timing, and exhaust gas recirculation (EGR) may be utilized in internal combustion engines in order to increase engine efficiency and fuel economy and decrease emissions including nitrogen oxides (NOx). One factor which may affect the efficiency of such operating parameters is ambient humidity. A high concentration of water in ambient air may affect combustion temperatures, dilution, etc. Therefore, control of operating parameters including air-fuel ratio, spark timing, EGR, and the like based on humidity can be used to improve engine performance.
U.S. Pat. No. 5,145,566 discloses a method to detect ambient humidity via an electrochemical oxygen pumping device. Specifically, the reference describes estimating an amount of EGR from the exhaust gas sensor in a way to eliminate errors caused by ambient humidity where the sensor reading is used with, and without, EGR flow in order to identify the amount of EGR. Further, the reference indicates that a separate sensor may also be used to measure ambient humidity, presumably by locating the second sensor outside of the exhaust gas.
The inventors herein have recognized, however, that during select conditions the exhaust gas sensor located in the exhaust gas of the engine can provide an indication of ambient humidity. Thus, in one example, a method for adjusting one or more of air-fuel ratio, spark timing, EGR, and/or the like in response to a measurement of the ambient humidity is disclosed. In one example, the method comprises generating an ambient humidity from an exhaust gas sensor during engine non-fueling conditions, in which at least one intake valve and one exhaust valve of the engine are operating and, under selected engine combusting conditions, adjusting an engine operating parameter based on the ambient humidity measurement.
In this manner, the effect of ambient humidity on various operating parameters may be reduced by using an exhaust gas sensor coupled in the engine exhaust to provide an indication of ambient humidity during select conditions. Further, in another example, an amount of EGR may be reduced during subsequent engine fueling operation as ambient humidity detected by the exhaust gas sensor increases in order to improve engine performance.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.